class Solution {
public:
    int mySqrt(int x) {
        if(x < 1) return 0;

        int left = 1, right = x;
        while(left < right)
        {
            long mid = left + (right - left + 1) / 2;
            if(mid * mid <= x) 
                left = mid;
            else
                right = mid - 1;
        }
        return left;
    }
};